How does Custom Datasource or Enhanced Datasource in GRC work?

In GRC - BW integration, the data in the GRC source system is first loaded into the data mart and further is extracted in in RSA3 to chk whether the data is loaded into the datasources.

SAP GRC - 10.0

SAP BW 7.40

Question: Can we create a enhanced/custom data source in GRC? How does the data mart function in Such a scenario? What changes needs to be done in the data mart so as to incorporate the data in the new enhanced/Custom data source?